This invention relates to turbomachinery and, specifically, to a system for supporting interchangeable upper and lower halves of a split, annular diaphragm radially in the steam path of a steam turbine.
Turbomachines generally comprise stationary and rotating parts defining a flow path for fluid through the turbine. Turbomachines also include an outer fluid tight caging called an outer shell from which a number of stationary parts, including split, annular diaphragms (that mount the fixed nozzles between the stages of the turbine), generally depend radially inwardly. In some prior arrangements, the diaphragms are positioned by radial keys (at the 6 and 12 o""clock positions) and are supported by support bars on opposite sides (in 9 and 3 o""clock positions) of the diaphragms.
The outer shell or casing may also be split along a horizontal joint so that the turbine shell comprises an upper half and a lower half. In building a turbomachine, certain stationary parts are mounted in the lower half shell whereas other stationary parts are mounted in the upper half shell while the two mating components are kept apart. The two halves are then assembled along a horizontal joint after the rotor has been mounted in the lower half.
As already noted, the diaphragms may likewise be split along a horizontal joint and comprise upper and lower diaphragm halves. The lower diaphragm halves are each mounted in the lower half shell, and after rotor installation, the upper diaphragm halves are bolted to the lower diaphragm halves. It is necessary, however, to align the diaphragm with the rotor to insure a uniform and desired radial gap between them.
Traditionally, large diaphragms have been supported radially by pads bolted to the sides of the lower half diaphragm, and supported by the lower turbine shell. The current design uses a rectangular slot and bolts to fasten the diaphragm support or pad to the diaphragm. With higher turbine power density designs in fixed outer shells, however, the available space for current supporting systems has become problematic. Supporting blocks or pads, hold down bolts, sealing keys and lifting holes, etc. all vie for the limited space.
In addition, with current designs, alignment of the diaphragms can only be achieved by removing the rotor from the shell. In addition, the lower halves of diaphragms are the last major maintenance component to be received, and the first to be reinstalled after repair. Current designs simply do not address serviceability concerns. There is thus a need for simplified diaphragm construction that reduces alignment time, errors, and minimizes crane usage for rotor removal, and that facilitates serviceability.
This invention provides a new system for supporting steam turbine diaphragms radially within the steam path. It also provides diaphragm alignment capability without removing the rotor from the casing. The new support system includes a support bar that incorporates a dovetail for mating engagement with a dovetail slot in the outer ring of the lower diaphragm half that carries the load and maintains radial position. This arrangement is provided on both sides of the diaphragm.
Specifically, the support bar in accordance with one exemplary embodiment of the invention includes a vertical body portion with an outwardly directed support flange at an upper end thereof, and an inwardly directed dovetail adjacent a lower end thereof. The supporting flange is adapted to engage a shoulder of the lower casing half via a plurality of adjustment shims, a shim pack clamping block, and a shim pack clamping bolt. The shims are employed to align the diaphragm as necessary, relative to the rotor. The dovetail is engaged with, or seated within, a mating dovetail slot formed in the diaphragm lower half, adjacent the split line (between the upper and lower diaphragm halves).
A set screw approximately mid-way along the support bar is used to stabilize the support bar relative to the lower diaphragm half, while an additional set screw extends through the dovetail itself, bearing on the base of the dovetail slot, thus enabling the dovetail joint to be securely locked.
In the exemplary embodiment, the upper and lower diaphragm halves are also made identical, so that each diaphragm half can be used as either the upper or lower half component. Thus, dovetail slots are formed in identical locations on both diaphragm halves so that the support bar described above will have a mating dovetail slot in whichever diaphragm half is used as the lower half. Similarly, the clamping bolt holes and bolt access arrangements for the support bars, as well as the joint bolts and bolt holes for securing the upper and lower diaphragm halves are also made identical.
The above described dovetail design eliminates the bolts and drilled holes in the outer ring of the diaphragm, and provides additional advantages with respect to design simplicity, flexibility, quicker and more accurate alignment, and decreased maintenance. Moreover, the design provides immediate servicing of the upper half of the diaphragm without waiting for the lower half to be removed. At the same time, the interchangeability feature permits assembly and alignment of the upper diaphragm halves in the lower position, again shortening outage duration. In addition, the direct alignment of turbine rotors with the stationary components (diaphragms) in the turbine shell, avoids alignment errors caused by translating data from other alignment techniques.
In its broader aspects, the present invention relates to a turbine diaphragm adapted to be supported in a lower turbine shell component comprising a first diaphragm half portion having a pair of diametrically opposed horizontal joint surfaces; a second diaphragm half portion having a similar pair of diametrically opposed horizontal joint surfaces; the first and second diaphragm half portions being identical, including identical mounting slots for receiving a support bar engageable with the lower turbine shell component to thereby insure interchangeability of the first and second diaphragm half portions.